From: Meng Xu <email@example.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Andrew Cooper <firstname.lastname@example.org>,
Wei Liu <email@example.com>,
Subject: Re: Question about Xen reboot on panic
Date: Thu, 12 Nov 2015 14:54:41 -0500 [thread overview]
Message-ID: <CAENZ-+kcXBWzamzc4cEVFSwq-GGYf7=WhrKGQac474mz3eySfw@mail.gmail.com> (raw)
2015-11-12 12:08 GMT-05:00 Jan Beulich <JBeulich@suse.com>:
>>>> On 12.11.15 at 17:57, <firstname.lastname@example.org> wrote:
>>> After looking into the code, I found the following code in the
>>> machine_restart(), which is quite suspicious.
>>> if ( system_state >= SYS_STATE_smp_boot )
>>> /* Ensure we are the boot CPU. */
>>> if ( get_apic_id() != boot_cpu_physical_apicid )
>> If we are at the boot CPU and the if statement return true
>>> /* Send IPI to the boot CPU (logical cpu 0). */
>>> on_selected_cpus(cpumask_of(0), __machine_restart,
>>> &delay_millisecs, 0);
>> we will send an IPI from CPU 0 to CPU to run machine_restart.
> The other way around you mean.
>>> for ( ; ; )
>> and CPU 0 will halt immediately.
>> If the IPI arrives later on CPU 0, CPU 0 won't be able to handle it,
>> since it has been halted.
> It's CPUn that gets halted, not CPU0. This ...
You are right. When system_state > SYS_STATE_smp_boot, CPU i (i != 0)
will send IPI to CPU 0.
>> (XEN) On P0
>> As this line suggests, P0 sends P0 an IPI and P0 goes to halt immediately...
> ... is suspicious: Is boot_cpu_physical_apicid not set correctly?
> Or is get_apic_id() returning rubbish?
After printing out the boot_cpu_physical_apicid and get_apic_id, I
found that are correct!
However, the line after that if statement is:
which is not in the if ( get_apic_id() != boot_cpu_physical_apicid ) statement.
So P0 may run this code, and from what I read from this
smp_send_stop(), it has the following code:
I'm guessing at __stop_this_cpu() when it is on P0, P0 will be
stopped. That's why P0 will never have the chance to proceed to the
rest of logic in the machine_restart(). Therefore, the machine won't
If I move this smp_send_stop(void) into the if statement, Xen will reboot.
Do you think this could be a fix?
If I misunderstood anything, please let me know...
PhD Student in Computer and Information Science
University of Pennsylvania
next prev parent reply other threads:[~2015-11-12 19:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-11 22:49 Question about Xen reboot on panic Meng Xu
2015-11-11 22:54 ` Andrew Cooper
2015-11-11 23:21 ` Meng Xu
2015-11-11 23:34 ` Andrew Cooper
2015-11-12 2:10 ` Meng Xu
2015-11-12 12:52 ` Andrew Cooper
2015-11-12 12:57 ` Wei Liu
2015-11-12 13:16 ` Ian Campbell
2015-11-12 15:09 ` Meng Xu
2015-11-12 15:07 ` Meng Xu
2015-11-12 16:13 ` Meng Xu
2015-11-12 16:57 ` Meng Xu
2015-11-12 17:08 ` Jan Beulich
2015-11-12 19:54 ` Meng Xu [this message]
2015-11-13 7:39 ` Jan Beulich
2015-11-19 3:58 ` Meng Xu
2015-11-19 7:26 ` Jan Beulich
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